вот, быстро накидал кода

лови:

Код AS1/AS2:
var p0:MovieClip = createPoint(170,270);
var p1:MovieClip = createPoint(300,100);
var a:MovieClip = createPoint(200,200);
var b:MovieClip = createPoint(300,200);
var c:MovieClip = createPoint(300,300);
var d:MovieClip = createPoint(200,300);
onEnterFrame = function()
{
_root.clear();
var hit:Boolean = true;
var dx:Number = p1._y-p0._y;
var dy:Number = p0._x-p1._x;
var s0:Number = (a._x-p0._x)*dx+(a._y-p0._y)*dy;
var s1:Number = (b._x-p0._x)*dx+(b._y-p0._y)*dy;
var s2:Number = (c._x-p0._x)*dx+(c._y-p0._y)*dy;
var s3:Number = (d._x-p0._x)*dx+(d._y-p0._y)*dy;
if( (s0> 0&&s1> 0&&s2> 0&&s3> 0)||
(s0<=0&&s1<=0&&s2<=0&&s3<=0))hit=false;
beginFill((hit)?0xff0000:0x00ff00);
moveTo(a._x,a._y);
lineTo(b._x,b._y);
lineTo(c._x,c._y);
lineTo(d._x,d._y);
endFill();
lineStyle(1);
moveTo(p0._x,p0._y);
lineTo(p1._x,p1._y);
}
function createPoint(x:Number,y:Number):MovieClip
{
var i:Number = getNextHighestDepth();
var p:MovieClip = createEmptyMovieClip("point"+i.toString(),i);
p.beginFill(0);
p.lineTo(7,0);
p.lineTo(0,7);
p.endFill();
p._x = x;
p._y = y;
p.onPress = function(){this.startDrag();}
p.onMouseUp = function(){this.stopDrag();}
return p;
}